Method for assembling two parts having accurate dimensions and use for brazing of a linac RFQ accelerator

ABSTRACT

A method of assembling two parts of which the dimensions of one of the parts or the final assembly are to be adhered to with precision. In the part whose dimensions are to be adhered to with the highest level of precision, a groove is machined to have a depth greater than a depth of a zone constituting a closed outline delimiting a space where the assembly exercises constraints, located between these dimensions and the zone, so as to introduce some elasticity.

TECHNICAL FIELD

The invention relates to a method of assembling, for example via thebrazing or soldering, of two parts of precise dimensions, and itsapplication to the brazing of a LINAC RFQ accelerator. The field of theinvention is that of mechanical precision engineering.

STATE OF THE PRIOR ART

The heating necessary for brazing engenders, after cooling, undesirablemodifications to the dimensions of these parts. The invention proposesto limit the effects of two types of interference convergent withreducing the precision of the dimensions of one of the parts or of thefinal assembly.

On one hand, a first type of interference is established, whether theparts to be brazed are of the same material or of different materials.

For example, the spreading of the heat during the brazing or solderingthermal cycle creates a thermal gradient introducing constraints anddistortions that, if they are plastic, remain irreparable and which aredifficult to control. This phenomenon is particularly critical if ittakes place near to the brazing zone or to severe tolerance zones forthe correct operating of the final object. Thus a section of a thinnerpart due to a recess or a bore can increase the undesirable thermalgradient because of the geometry.

Another example is the releasing of the internal constraints of thematerials, provoked by the high temperatures.

A result of these two phenomena can be uneven micro-distortions thatsubstantially modify some dimensions of the part.

On the other hand, a second type of interference is established duringthe brazing or soldering of the two parts comprised of differentmaterials, bearing different dilatation coefficients. During the coolingafter the brazing, the parts assembled and thus integral, try to returnto their initial positions. Also, they pull on each other, thus inducinga series of constraints that mutually distort them.

We will only consider cases when the brazing or soldering zone makes aclosed curve, even if it is in a discontinuous manner. Such a curvedelimits an internal zone and an external zone.

Without restricting ourselves to this case, the benefits of theinvention are more obvious when we consider the case when one of theparts has, on a same side of the brazing zone (either in the internalzone or in the external zone), dimensions that must be adhered to aswell as a recess or bore of sufficiently large dimensions, asillustrated for example in FIGS. 1 and 2. FIG. 1 represents a partcomprising on the inside of a brazing zone 6 several dimensions, forexample a and b, that are to be adhered to with precision and atriangular recess 7, with dimensions comparable to the dimensions ofthis brazing zone 6. FIG. 2 represents a part comprising on the outsideof a brazing zone 6 dimensions c and d that are to be adhered to withprecision and a bore 8 with dimensions comparable to the dimensions ofthis brazing zone 6. In such cases, the interference of the first typedescribed above induces micro-distortions that prohibit the maintainingof the precise dimensions a, b, c and d obtained after machining.

The distortions can also be caused by the interference of the secondtype described above, when the two metals to be brazed are not of thesame quality and behave differently depending on the temperature.

The distortions are greatest when interference of the two typescumulates. In extreme cases with at least strong interference of thesecond type, the micro-distortions can even lead to fracturing withinthe assembly.

The general brazing techniques are highlighted in the document marked[1] at the end of the description, however the precise adherence to thedimensions is not covered in this document.

The difficulty in correctly planning the behaviour of a unit to bebrazed lies in the large number of parameters which are involved: thedilatation coefficients, the mechanical properties of the materials inthe elastic and plastic fields which furthermore evolve according to thetemperature, the dimensions obtained after machining, the clearancesbetween the parts to be brazed, etc. This number of parametersmultiplies, of course, if the chosen solution uses several brazingstages.

The question of rigidity of an assembly thus obtained when the materialshave different dilatation coefficients opens out to two types oftechniques.

The first group is based on the elasticity of an intermediary layerplaced between the parts to be assembled. The document marked [2] thusdescribes a method to braze a part made in carbon with a metal heatdissipater. The difference in dilatation is then noticeable as it has acoefficient of about 10.

The document marked [3] describes a method in which we insert a ringthat plastifies between the two parts to be brazed, by using thesuper-plasticity of some materials. A typical example of such atechnique consists in brazing a copper ring to the inside diameter of astainless steel flange and then brazing this unit to the copper part tobe brazed. The ring has the same dilatation coefficient as the part tobe brazed but the first brazing stage makes it possible to create alocalised plastic zone that does not then spread to the definitive part.

Another solution consists in inserting one or several layers ofmaterials with an intermediary dilatation coefficient between the twoparts to be brazed.

The second group is based on the adding of a discontinuous resilientstructure between the two parts to be brazed, as described in thedocument marked [4].

A plastic ring composed of a material softer than at least one of theparts to be assembled can likewise be inserted between these two parts.In the document marked [5], we increase the plasticity of such a ring bycreating indentations on one part and asperities on the other part. Theinsertion of a distortable ring makes it possible to substantiallyreduce the positioning errors introduced through brazing, but under nocircumstances makes it possible, even with the cited developments, toobtain a precise assembling that does not considerably deteriorate theprecise machining of each part.

These documents are not aimed at preserving precise dimensions duringbrazing. In particular they do not provide any lessons regardinginterference of the first type, that meaning in the case when one of theparts has, on a same side of the brazing zone, dimensions that must beadhered to with precision as well as a recess of non-negligibledimensions in relation to the dimensions of this zone. If we refer toFIGS. 1 and 2, these methods induce micro-distortions that do not makeit possible to precisely maintain the dimensions a, b, c and d obtainedafter the machining.

The precise adherence to these dimensions thus requires re-machining,which is costly and sometimes delicate or impossible to perform.

By way of example of application, we can cite the linear accelerators ofionised particles of LINAC RFQ (“Radio Frequency Quadrupole”) type, andmore particularly the models characterised in that the four pole partshave a vane structure and not made as for lower powered models usingconducting rods of variable diameter. A LINAC RFQ of this type has acentral casing of approximately tubular shape, made in copper. Moreprecisely, its overall shape is that of a conoid whose outer surface isnearly that of a cylinder, and whose inner surface has four poleoutgrowths extending radially towards the centre, without howeverreaching it. The free central axis allows for the circulation of theparticles which thus run along the four poles. This casing is to bebrazed at each end to a mounting flange, in stainless steel, whichsurrounds it.

The positioning of the axis of symmetry is to be done with the highestlevel of precision in relation to the devices fixed both upstream anddownstream. But it is even more important not to induce, via brazing, acrushing constraint which would modify the distances between the ends ofthe poles facing each other, as these distances are crucial for theoperating of the accelerator, this being all the more so as the complexgeometry of the unit renders any re-machining impossible.

The other existing vane structured RFQs either accept markedly largerprecision or use flanges in glidcop, a copper-based alloy that has itsthermal behaviour. The making of such RFQs is described in the document[6]. This document, itself, makes no mention of the thickness of thejoints. However, FIG. 2 shows that the mounting flanges have a thicknessof 0.5″ (that being 12.5 mm), which for those skilled in the artindicates a low tightening torque and thus the use of metal joints.Indeed, a high tightening force would be the origin of a high torquebetween its contact point and that of the seal, inducing a redhibitorydistortion of the flange.

The inconvenience is therefore the obligation to use low tighteningtorque seals, thus made of polymers, such as Vitron, which do not makeit possible to create as high a vacuum within the chamber. The inventionmakes it possible to use metal joints deemed better, even indispensablefor ultra-high vacuum.

We are not aware of any other embodiment of a vane structured RFQ andstainless steel flanges, allowing the use of metal joints.

The purpose of the invention is to overcome the inconveniences of thedocuments of the known art thus making it possible to obtain in the casewhen one of the parts has, on a same side of the brazing zone,dimensions that must be adhered to with precision, as well as a recessof non-negligible dimensions in relation to the dimensions of this zone,precise dimensions after an assembling of two parts via brazing, this inorder to obtain a precise assembling that does not considerablydeteriorate the precision machining of these parts, even if these partsare in different materials.

PRESENTATION OF THE INVENTION

The invention proposes a method of assembling, via brazing or soldering,two parts of which the dimensions of one of the parts or the finalassembly are to be adhered to with precision, characterised in that wemachine beforehand, in the part whose dimensions are to be adhered towith the highest level of precision, a groove of depth p greater thanthe depth p_(br) of one zone, for example the brazing zone, constitutinga closed outline delimiting a space where the assembly exercisesconstraints, located between these dimensions and said zone, so as tointroduce some elasticity.

The invention indiscriminately applies when the micro-distortionsdescribed above are of the first or the second type, but it isparticularly recommended when these two types cumulate.

Preferably, we insert between the two parts a malleable ring.

The invention has numerous benefits. Firstly it makes it possible toavoid that the operation of brazing or soldering, and the consequentialconstraints, induce a loss of precision for the dimensions to be adheredto. It also makes it possible to guarantee a high level of precision inthe relative positioning of the two parts to be assembled, which isgenerally advantageous when they share the same axis of symmetry. In thecase when one of the parts has a bore that has precise dimensions to beadhered to, the invention allows this dimension not to be penalisedduring the brazing operation. The invention allows such precisionassembly even when the different parts are made in different materials.

When a precise dimension has to be made in an inaccessible area with atool for re-working, the recourse to the invention proves to beindispensable. In a standard case, it does away with mechanicalre-working therefore assembly on a machining tool, which reduces thecost of the finished part.

By adding to the malleable ring, between the brazing zone and theelement whose dimension is to be adhered to, a machined groove to one ofthe parts, the method according to the invention makes it possible toobtain an improved precision assembly in comparison with the prior art.It generates an auto-centring effect, synergetic to the plasticdistortion introduced by the ring.

The position and the depth p of this machined groove must be optimisedto obtain the best results. The position of the groove is not verycritical. It must above all lie between the brazing and the zone,generally bored out, the dimensions of which we want to maintain withprecision. It must also be sufficiently close to the zone to be brazedso that the elasticity it induces is effective, but sufficientlydistanced from this zone so as to ensure the mechanical aspect of thepart. Those skilled in the art will easily find a position that respectsthese conditions.

The depth p is harder to optimise. It is dependent on the depth p_(br)of the brazed zone, and increases in accordance with the increase indepth. It must be greater than p_(br) and preferably lie between 2 and 3times the depth p_(br) of the brazed zone.

The setting, and if need be the optimising of the parameters of thisgroove, is performed through trials in the case of simple andinexpensive parts. For complex and costly parts, as well as when we wantto obtain a high level of precision, for example of about a fewhundredths of a millimeter, or a precision greater than the machiningprecision, it is performed using a mechanic CAD code (Castem or Ansysfor example) used repeatedly according to the following stages:

1. guesswork evaluating of a position and a groove depth which seemreasonable, the depth p being greater than the depth p_(br) of the zoneto be brazed;

2. modelling, for each of the two parts, of the effects of the rise intemperature, until reaching the brazing temperature, notably taking intoaccount the differences in the dilatation coefficients of the materials;

3. when the calculation arrives at a high temperature, the insertion ofa manual cell bonding stage when the parts come into contact so as toreconstitute in a continuous manner the cells of the two parts that areto be in contact;

4. modelling of the drop in temperature;

5. checking of the value of the induced constraints, which must remainacceptable, otherwise correction of the depth of the groove (possibly ofits position) and a further repeat of the above stages.

The groove being thus defined, we then carry out the brazing itself.

Advantageously, when several brazings are to be performed, or when theshape of the part is complex, we simultaneously carry out all thebrazings by placing the filler metal so that, as it is liquid duringbrazing, it runs between the surfaces that are to be brazed. The fillermetal is either in the form of a leaf a few micrometers thick insertedbetween the two surfaces to be brazed or in the form of wire placedinside shallow grooves, called “brazing grooves”, previously machined inone of the parts. Then the unit is placed inside a furnace, which meltsin a single operation the filler metal, which makes the variousbrazings.

Such furnace-made brazings are generally necessary so as to obtainprecision assemblies of about a few hundredths of a millimeter. Howeverto obtain the highest level of precision, it is to be used in atwo-stage process as we will present in the detailed embodiment of theLINAC RFQ.

Following the brazing itself, we place the resulting assembly on ametrological apparatus to read the dimensions and we define the actualcentre of the bore using a mathematical method, for example that ofleast squares. This centre is defined in relation to previously mademarkings, and which must themselves be defined with sufficientprecision.

The method of the invention can advantageously be used to carry out aLINAC RFQ accelerator. It is particularly advantageous if this LINAC isa vane structure type. In this case the casing of the accelerator is aunit of four pole parts, generally formed of four sectors that areroughly cylindrical, each of which support one of the four poles. Thehighest level of precision is obtained via the implementation describedbelow, which optimises the performances of the invention and constitutesthe optimal realisation. In a first stage, we assemble via soldering orbrazing the elastic ring at each end to the corresponding flange. In asecond stage, we read, using a metrological apparatus, the dimensions ofa set of pre-determined points and we search via calculations the actualposition of the bore axis. In a third stage, this position is used tocentre the four pole parts, prior to the last stage consisting inmelting the weld bead. Such a technique allows for precision greaterthan that resulting from the machined precision of each part and of theclearances accepted for its installation.

Once the characteristics of the groove have been defined, the followingstages are carried out:

1. defining of a reference base, defined on the drawing;

2. machining according to this base of the different parts with theirgroove, layout of highly precise physical markings (slugs), thenbrazing;

3. controlling with a metrological apparatus, in order to read thedimensions of a list of predetermined points, their co-ordinates beinggiven in the reference base;

4. searching via the least squares method for the actual position of thebore and defining of a new centre, and therefore of a new base (theinvention supposes that the bore is correct but that its actual centremay be offset);

5. the off-setting between the first marking and the second marking istaken into account when expressing in the new base the co-ordinates ofthe initial markings; they become the references which make it possibleto centre the part.

The part is thus centred in relation to the second base.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 diagrammatically represent two types of parts to which theinvention could be applied: FIGS. 1A and 1B respectively represent afront view and a cross section view AA of a first type of part, in whicha recess is located on the inside of a brazing zone, and FIGS. 2A and 2Brespectively represent a front view and a cross section view BB of asecond type of part, in which a recess is located on the outside of abrazing zone.

FIG. 3 illustrates the production of an assembly via brazing, accordingto the invention, of two parts with an axial symmetry;

FIG. 4 illustrates a simplified view of the end of a LINAC RFQ typeaccelerator;

FIG. 5 illustrates the obtained assembly of the casing of such anaccelerator on two flanges according to the method of the invention;

FIG. 6 illustrates the genuine production of the casing of such anaccelerator, constituted of four elements.

DETAILED PRESENTATION OF EMBODIMENTS

The method of the invention is a method of assembly, for example viabrazing or soldering, of two parts with precise dimensions, for exampleof two parts with axial symmetry and made in different materials.

As is illustrated in FIG. 3, the method of the invention consists in:

-   -   possibly inserting a malleable ring 12 between a first part,        which in this case is a part 10 with axial symmetry with a        recess 14, and a second part, which is a flange 11;    -   and machining, prior to assembling, a calibrated groove 13 in        one of the two parts, the depth p of this groove depending on        the depth p_(br) of the brazed zone, and being longer than it,        and preferably comprised between 2 and 3 times p.

In the case when the requested precision is sufficiently low so as notto request a modelling via a mechanic CAD code, such a production makesit possible to avoid the need to know the exact difference in thedilatation coefficients between these two parts 10 and 11.

When we aim for high tolerances, the method of the invention is appliedavoiding all quantitative studies and precise machining to obtainprecise assembling which does not considerably deteriorate the precisionmachining of the surfaces to be brazed.

On the contrary, when we aim for severe tolerances, the parameters canbe optimised, possibly through tests, but preferably with the use of theaforementioned modelling.

Such a procedure supposes a specific use of the calculation codes. Whenthe calculation arrives at a high temperature, with the taking intoaccount of the characteristics of the materials, this usage consists ininserting a manual cell bonding stage when the parts come into contact.

Other and above the benefit of satisfying the desired objective, themachining of such a resilient groove 13 has the benefit of minimisingthe releasing, during a brazing thermal cycle, of the constraintsgenerated in the material during its elaboration.

An advantageous application of the method of the invention relates to alinear accelerator of RFQ type such as is described in the documentmarked [7].

Such an accelerator comprises a tubular part, or accelerator casing,whose external section is octagonal and which comprises, on the inside,four pole outgrowths extending radially towards the centre, withouthowever reaching it. On their surface facing the centre these poles areequipped with undulations distributed symmetrically for the two poles ofa same plane, and offset by a half-period between a pole and the polethat immediately follows it on a longitudinal profile. This casing is tobe brazed at each end on two circular flanges connecting it to thedevices located upstream and downstream. After this brazing, thealignment of the symmetry axis is to be done with the highest level ofprecision in relation to these devices located at the ends. But it iseven more important not to induce, via brazing, a crushing constraintthat would modify the diameter of the bore at the centre of the casing,as that would modify the relative position of the pole ends facingtowards the inside. Furthermore, this position is crucial for theoperating of the accelerator. The casing geometry renders allfinish-machining or corrective-machining impossible after the brazingoperation.

In order to ensure good vacuum tightness, we envisage placing metaljoints between two removable parts. This choice leads to the use ofstainless steel flanges, the copper not being sufficiently rigid tosupport the necessary tightening forces of this type of joint. Aselsewhere, the structure is in copper, the brazing of the flange on theaccelerator casing involves the use of two distinctive materials.

The method of the invention can advantageously be used for theproduction of such an accelerator, of which one end is diagrammatised inFIG. 4 with notably the pipes 21 allowing the circulation of a coolingflux, the axis 22 being the beamed particle axis as well as the symmetryaxis, the first part with axial symmetry to be brazed here being thecasing 25 and the second part to be brazed being the flange 26, the fourpoles being marked 30.

FIG. 5 illustrates the unit obtained by thus assembling the coppercasing 25 onto two stainless steel flanges 26 according to the method ofthe invention, the malleable ring 27 being a copper ring, the groovebeing marked 28. The groove 29 illustrated in this figure is used tointroduce a high frequency joint.

The essential requirements for the production of such an accelerator arein order of priority:

-   -   the symmetry of the poles according to the longitudinal and        transversal axes;    -   the average adjacent distance between the poles;    -   the alignment of the poles from one section to the other;    -   the distance between the poles correct on all points.

These essential requirements translate into tolerances on the pole axesand shape tolerances on the internal surface of the quadrants (end ofthe poles located near the axis):

-   -   the shape tolerance of the poles: 0.02 mm;    -   the shape tolerances at the bottom of the cavity: 0.05 mm;    -   the perpendicular aspect between the two poles: (0.02 mm/200        mm).

In normal position, the beam axis seen by each pole is mixed with theothers. The ends of the poles located towards the beam are laid out insquares in a section according to a plane transversal to the axis.Nevertheless, the two poles located in one plane are axially offset byhalf an undulation in relation to the two poles located in theorthogonal plane. Thus when the cross section plane moves axially, thisfigure created by the pole ends located towards the beam successivelyforms a square, a rhombus whose large axis is vertical, a square, arhombus whose large axis is horizontal, a square, and so forth.

The two planes of symmetry are to be adhered to by +/−0.01 mm. Adistortion forming a rhombus is acceptable.

To restrict the distortion of the rhombus, we add a positioningtolerance of the pole axis in relation to the axis of the beam in theform of a shape tolerance of the ruled surface, which constitutes theend of the poles.

A simple calculation presuming a dilatation difference of 1.10⁻⁶ whichis very small and to be specific corresponds to the measurement limit ofthis type of parameter, shows that in the given dimensions the brazingshould induce a distortion of about 0.1 mm.ΔL=140 mm×1.10⁻⁶×1000° C.=0.14 mm

Furthermore, we saw that we aimed for distortions of about 0.01 mm. Thedifference between the desired value and the dilatation coefficientclearance offers a large freedom of movement for parasite phenomena.

The method of the invention makes it possible to satisfy such essentialrequirements. The method of the invention then comprises two brazingstages. The first stage is a brazing stage of one of the parts, thestainless steel flange 26, with the intermediary copper ring 27. Thisintermediary part is sufficiently thin to undergo distortions from thefirst part. The second stage is a brazing stage of this unit with thecopper accelerator casing 25.

The casing thus defined is not practically feasible in one part. It isin fact made of four parts, and the brazings are all done together usinga furnace as mentioned above.

FIG. 6 illustrates the actual constitution of the casing 25 of such afour-part accelerator (31, 32, 33 and 34). Indeed, according to theinvention, the parts to be brazed are not necessarily monolithic. Theaccelerator casing, which is centrally positioned, is actually made offour parts.

More precisely, the accelerator requires on one hand the assembling offour elements together, which is done without the need for a ring and agroove according to the invention but via a furnace brazing, and at eachof the ends of this unit a brazing according to the invention, with ringand groove with a depth of 2 to 3 times p. But prior to this, each ofthe copper rings has been individually brazed to one of the stainlesssteel flanges, then the inside of each ring has been corrected beforecarrying out in a second stage the assembling in the furnace of all ofthe four vane structure parts with the end flanges.

For this second stage, over all the surfaces to be brazed, we place in a“brazing groove” machined on one of the parts, not represented in FIG.6, a wire constituted of the filler metal, then the unit is placed in afurnace which melts the filler metal and simultaneously produces thecorresponding brazings.

The method of assembling according to the invention is particularlyadvantageous for the assembling of LINAC RFQs. It however remainsapplicable to all types of LINACs, as well as applications requiringless precision, such as travelling-wave tubes, even some klystrones.

The invention can be applied generally in all cases when a method ofassembling defines a zone constituting a closed outline delimiting aspace where the assembly exercises constraints, comparable in this wayto the brazing zone, on the inside of which are dimensions that are tobe adhered to with precision as well as at least one recess ofnon-negligible dimensions in relation to the dimensions of this zone. Itcan thus be transposed to a tight fit, in which a central part istightly held by the other part whose internal diameter is slightly toosmall. To produce such a tight fit, we heat the external part, or weenergetically cool the central part, or we even simultaneously applythese two treatments. Once back to thermal equilibrium, the central partis well fixed, and in a certain manner compressed by the part which isclamping it. The invention can then be applied to create on the centralpart a zone where the constraints are lower and the dimensions bettercontrolled.

REFERENCES

-   -   [1] “Constructions soudées, brasage” [Soldered, Brazed        Structures] by Léon Noël (Engineering Techniques, marked B 5195)    -   [2] U.S. Pat. No. 5,855,313

[3] U.S. Pat. No. 5,289,965

-   -   [4] U.S. Pat. No. 2,707,540    -   [5] U.S. Pat. No. 5,501,390    -   [6] “CW RFQ Fabrication and Engineering” by D. Schrage, L. Young        and al. (Los Alamos National Laboratory, conference LINAC 1998)    -   [7] “Proton Linear Accelerators, A Theoretical and Historical        Introduction” (Los Alamos, LA-11601-MS, July 1989)

1. A method of assembling, by a brazing or soldering, two partscomprising the following step: machining, prior to assembly, anelasticity groove in one of the two parts, dimensions of the one parthaving to be maintained with precision, wherein said elasticity grooveis situated between a first zone of constraints created by operation ofbrazing or soldering between the two parts and a second zone thedimensions of which must be maintained with precision, and wherein saidelasticity groove has a depth formed between 2 and 3 times the depth pbrof the first zone of constraints.
 2. A method set forth in claim 1,further comprising inserting a malleable ring between the two parts. 3.A method set forth in claim 1, applied to two parts of which one has, ona same side of the first zone of constraints, dimensions that must beadhered to with precision and at least one recess.
 4. A method set forthin claim 1, applied to two parts whose dilatation coefficients aredifferent.
 5. A method set forth in claim 1, wherein the groove is madeon one part of the assembly located at a center.
 6. A method set forthin claim 1, wherein the groove is made on one part of the assemblylocated at a periphery.
 7. A method set forth in claim 1, wherein allbrazings are simultaneously performed in a furnace.
 8. A method ofassembling a succession of two parts joined in twos according to themethod set forth in claim 1, wherein a filler metal is placed in contactwith each twos of parts to be assembled, and the unit is held inposition and placed in a furnace that melts in a single operation thefiller metal, and performs brazings.
 9. A method of assembling a set ofparts comprising a central element itself including plural parts,connected at each of their ends by a part that surrounds the pluralparts, wherein only brazings between end parts and the central parts areperformed according to the method set forth in claim
 1. 10. Use of themethod set forth in claim 1 for producing a LINAC RFQ type accelerator.11. A method of assembling, by a brazing or soldering, two parts ofwhich dimensions of one of the two parts or of a final assembly are tobe adhered to with precision, comprising: machining in the one partwhose dimensions are to be adhered to with precision, before assembling,a groove to have a groove depth greater than a depth of a zoneconstituting a closed outline delimiting a space where the assemblingexercises constraints, located between the dimensions and the zone, tointroduce some elasticity; and inserting a malleable ring between thetwo parts, wherein the malleable ring is firstly brazed or soldered toone of the parts, then corrected for at least one of the dimensions tobe adhered to, then brazed or soldered to the other of the parts. 12.Use of the method set forth in claim 11, wherein the LINAC RFQ typeaccelerator is of vane structure.
 13. A method of assembling, by abrazing or soldering, two parts of which dimensions of one of the twoparts or of a final assembly are to be adhered to with precision,comprising: machining in the one part whose dimensions are to be adheredto with precision, before assembling, a groove to have a groove depthgreater than a depth of a zone constituting a closed outline delimitinga space where the assembling exercises constraints, located between thedimensions and the zone, to introduce some elasticity, whereinparameters of the groove are defined using distortion simulations by amechanic code by reproducing each of principal brazing stages of: (a)judge rating of a position and the groove depth which seem reasonable,the groove depth being greater than the depth of the zone; (b)modelling, for each of the two parts, effects of a rise in temperature,until reaching a brazing temperature, taking into account a differencein dilatation coefficients of materials; (c) controlling with ametrological apparatus, to read dimensions of a list of predeterminedpoints, their co-ordinates being given in a reference base; (d)searching by least squares method for an actual position of a bore anddefining a new center, and therefore a new base; (e) off-setting betweena first marking and a second marking is taken into account whenexpressing in the new base co-ordinates of initial markings; whichbecome references that make it possible to center the part.